Problem: Michael ate 3 slices of pie. Omar ate 5 slices. If Michael ate $\dfrac{3}{9}$ of the pie, what fraction of the pie is remaining?
If 3 slices represent $\dfrac{3}{9}$ of the pie, there must have been a total of 9 slices. $\text{fraction of pie remaining} = \dfrac{\text{number of slices remaining}}{\text{number of slices total}}$ Together they ate 8 slices, which leaves 1 out of 9 slices remaining. There is $\dfrac{1}{9}$ of the pie remaining.